Sampling systems, such as digital oscilloscopes, sample and display characteristics of various types of applied waveforms. One type of waveform that may be applied to a sampling system, a single-valued waveform, is repetitive in time. Multi-valued waveforms, such as random or pseudo-random digital streams present in communication networks, may also be applied. Alternatively, noise, rather than single-valued or multi-valued waveforms, may be applied to the sampling system.
Automatic adjustment of system parameters, or auto-scaling, enables users of the sampling system to observe the characteristics of the applied waveform displayed on a monitor or other output device. For example, automatic adjustment of amplitude gain and offset parameters (amplitude auto-scaling) vertically positions the sampled representation of the applied waveform on a digital oscilloscope""s monitor so that amplitude characteristics of the waveform can be displayed. Similarly, automatic adjustment of time gain and offset parameters (time auto-scaling) horizontally positions a sampled representation of the applied waveform so that timing characteristics of the waveform can be displayed.
While automatic adjustment of system parameters is generally difficult within a sampling system when there are various types of waveforms that may be applied to the system, time auto-scaling is especially difficult to achieve. Auto-scaling methods that detect one type of event, such as zero-crossings within the applied waveform, are suitable for establishing and adjusting time gains and offsets for single-valued waveforms, but the methods may be unsuitable for establishing and adjusting time parameters for multi-valued waveforms, which generally lack repetitive zero-crossings. Each type of waveform applied to the sampling system requires detection of a different type of event for time auto-scaling. There is a need for a method that automatically scales a sampled representation of an applied waveform, regardless of whether the waveform is single-valued or multi-valued in nature.
An auto-scaling method constructed according to the preferred embodiment of the present invention auto-scales a sampled representation of an applied waveform, regardless of the nature of the waveform. The method, implemented within a digital oscilloscope or other type of sampling system, achieves amplitude auto-scaling from samples of the applied waveform acquired when the sampling system is un-triggered. The method then determines the nature of the applied waveform based on the number of acquired samples within an intermediate amplitude band and the number of amplitude transitions across the amplitude band. Records are then taken with the sampling system triggered and the occurrence of alternative designated events, based on the nature of the waveform, is detected within the records. Time offset and time gain are adjusted based on a first occurrence and a second occurrence of the designated events.